CODEWITHSUNDEEP
c++templatesstlcontainerstemplate-specialization
dguan
dguan

Reputation: 1033

How should I define this complex function template?

I need to define a function, the function takes two parameters, the first is a container which contains some containers of type T, the second is an integer, the function's signature may look like this:

#include <vector>
#include <string>
#include <list>

using namespace std;

vector<vector<T>> my_function(const vector<vector<T>>& var, int cnt);
vector<list<T>> my_function(const list<vector<T>>& var, int cnt);

how should I define the function template?

Upvotes: 3

Views: 139

Answers (3)

Abhishek Mittal
Abhishek Mittal

Reputation: 366

I have shared some code which defined the functions in a neater and readable manner.

template <typename T>
class MyClass {
    typedef vector <T> ContainerVecT;
    typedef list <T> ContainerListT;

    typedef vector <ContainerVecT> MyContainerVecT;
    typedef vector <ContainerListT> MyContainerListT;

    MyContainerVecT my_function(const MyContainerVecT& var, int cnt);
    MyContainerListT my_function(const MyContainerListT& var, int cnt);
};

Please let me know if it does not satisfy your requirement. We will work on that.

Upvotes: 0

R Sahu
R Sahu

Reputation: 206707

You can define the function as:

template<template<class> class outer,
         template<class> class inner,
         class element>
outer<inner<element>> my_function(
    const outer<inner<element>>& var, int cnt) {
  outer<inner<element>> ret;
  (void)var, (void)cnt;
  return ret;
}

However, you cannot call the function with the following lines:

std::vector<std::vector<int>> v;
my_function(v, 0);

or

my_function<std::vector, std::vector, int>(v, 0);

since std::vector is defined using more than one template parameter. One work around to that problem is to use:

template <typename T>
using MyVector = std::vector<T>;

Then, you can call:

MyVector<MyVector<int>> v;
my_function<MyVector, MyVector, int>(v, 0);

Still trying to figure out why

MyVector<MyVector<int>> v;
my_function(v, 0);

doesn't work.

Upvotes: 0

Deduplicator
Deduplicator

Reputation: 45684

This does what you say you want.
Now, you know what kind of containers might be used, and you might even be able to do something worthwhile with it...

#include <vector>

template<class X> class Y{};

template<template<class outer, class... x>
  class inner, template<class element, class... x> class outer,
  class element, class... x>
inner<outer<element, x...>, x...>
my_function(const outer<inner<element>>& var, int cnt) {
  inner<outer<element, x...>, x...> ret;
  (void)var, (void)cnt;
  return ret;
}

int main() {
#if 1
    const std::vector<std::vector<int>> x;
#else
    const Y<Y<int>> x{};
#endif
    my_function(x, 0);
}

Coliru: http://coliru.stacked-crooked.com/a/bb06e39c799e3b5e
Further reading: Template Template Parameters

Upvotes: 1

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